Hi, Lee-
I'm not aware of any way to do this without VBA code- so I wrote the
following code to do that task. Copy and paste this into your file as a
macro. This will create a formula that references cell A20 from each
tab in the workbook. You should try this out on a backed up copy of
your data to avoid catastrophic data loss.

Sub Three_D_Tab_Formula()
Dim SheetName As Worksheet

For Each SheetName In Sheets
ActiveCell.Formula = "='" & SheetName.Name & "'!a20"
ActiveCell.Offset(1, 0).Select
Next SheetName

End Sub